The present invention relates to control technique for controlling valve events of an engine with an actuator such as solenoid actuator, and in particular to control of an intake valve closing timing to vary an intake air quantity to obtain a desired engine torque.
Unlike an engine of a conventional type controlling the intake air quantity with a throttle valve, an engine of a new type (proposed by a Published Japanese Patent Application, Kokai No. H10(1998)-37727) is arranged to control the intake air quantity mainly by controlling the intake valve closing timing.
An intake air control system of such a type for controlling the intake air quantity by controlling the intake valve closing timing achieves a target air quantity (required intake air quantity) corresponding to required torque by controlling the volume of cylinder intake air corresponding to an effective intake stroke determined by the intake valve closing timing, at the intake pressure that is held approximately constant at the atmospheric pressure in the absence of a throttle valve, and that is determined in dependence on the throttle opening when there is provided a throttle valve.
To control the intake air quantity accurately by controlling the intake valve closing angle, the intake valve is to be closed at a piston position at which the cylinder contains an amount of fresh air corresponding to the target air quantity in addition to an amount of residual gases (internal EGR quantity) remaining in the combustion chamber. The internal EGR quantity of residual gases is influenced deeply by the existence or nonexistence of valve overlap and the length of valve overlap. The valve overlap condition has a great influence on the internal EGR quantity especially in a solenoid type valve actuating system having such a high response speed in opening and closing valves that the exhaust and intake valves are both held approximately in the fully open state during a valve overlap period. Accordingly, it has been found that simple correction or compensation for the internal EGR quantity is not always adequate for controlling intake air quantity and hence engine torque accurately. Moreover, even by a system devised to set target exhaust valve closing timing and target intake valve opening timing to obtain a proper internal EGR quantity and to adjust the target intake valve closing timing in conformity with the setting of the valve timings, an adequate control is difficult since the actual internal EGR quantity is affected by other factors besides valve timings.
It is, therefore, an object of the present invention to provide control apparatus and/or method capable of controlling the intake valve closing timing accurately and thereby controlling the intake air quantity and hence engine torque adequately.
According to the present invention, a control apparatus for controlling an intake air quantity to the engine by varying an intake valve closing timing of the engine comprises a controller that is configured or programmed:
to calculate a target air quantity in accordance with an engine operating state,
to calculate an estimated internal EGR quantity of the engine in accordance with the engine operating state,
to calculate a target intake valve closing timing in accordance with the target air quantity and the estimated internal EGR quantity, and
to control an actual intake air quantity to the engine by controlling an actual intake valve closing timing of the engine to achieve the target intake valve closing timing.
A control apparatus according to one aspect of the invention comprises: means for determining the estimated internal EGR quantity; means for determine the target intake valve closing timing in accordance with at least the estimate internal EGR quantity; and means for controlling the intake air quantity to the engine by controlling an actual intake valve closing timing of the engine to the target intake valve closing timing.
According to the present invention, a control process for varying valve timings of intake and exhaust valves of an engine, comprises: estimating an internal EGR quantity in accordance with an engine operating state; and controlling an intake valve closing timing in accordance with a required intake air quantity and the internal EGR quantity.